1. Field of the Invention
The present invention relates to an electric-powered air release valve that is particularly suitable for use in an exhaust device for a blood pressure gauge, and to a blood pressure gauge that comprises the electric-powered air release valve.
2. Description of the Related Art
A blood pressure gauge measures blood pressure during the process of gradually reducing the pressure inside a cuff belt after the pressure is increased to a prescribed value. In such a blood pressure gauge, an electric-powered air release valve is used to gradually reduce the pressure inside the cuff belt.
The electric-powered air release valve described in Japanese Patent No. 3029073 is known as a conventional example of an electric-powered air release valve used in a blood pressure gauge. This electric-powered air release valve has a movable coil, and is configured as shown in FIG. 7.
In FIG. 7, the reference numeral 201 indicates the main housing, and 202 indicates the front housing. An airflow channel 203 that passes through a pump, a cuff belt, or the like is provided to the front housing 202 that blocks an opening at the front end of the main housing 201, and one end of the airflow channel 203 leads into the main housing 201 and forms an opening as an air outflow vent (air release vent) 204.
An armature 220 as a movable element is provided in the center inside the main housing 201, and a permanent magnet 210, and yokes 211, 212 are provided on the external periphery of the armature 220. A drive coil 225 installed on the armature 220 is inserted between the yokes 211, 212, and the coil 225 is shaped so as to intersect the magnetic field between the yokes 211, 212.
The head of the armature 220 faces the center of the front housing 202, and a rubber valve (orifice gasket) 230 for opening and closing the air outflow vent 204 is provided to the head so as to face the air outflow vent 204. The armature 220 is also supported in the main housing 201 by two leaf springs 241, 242 at both ends in the movement direction, and is urged by the leaf springs 241, 242 in the valve-opening direction, i.e., the direction in which the rubber valve 230 is separated from the air outflow vent 204.
When blood pressure is measured using this electric-powered air release valve, an electric current that intersects the magnetic field between the yokes 211, 212 is first fed to the coil 225 by supplying electrical power to the drive coil 225. A drive force is then generated in the coil 225, the armature 220 moves against the urging force of the leaf springs 241, 242, and the rubber valve 230 closes the air outflow vent 204. In this state, air is fed into the cuff belt by a pressurizing pump, and the cuff belt is pressurized.
The process of reducing the pressure in the cuff belt then begins. At this time, the drive force generated in the drive coil 225 is continuously weakened by gradually reducing the current fed to the coil 225. The armature 220 is then moved toward the initial position by the urging force of the leaf springs 241, 242, the rubber valve 230 separates from the air outflow vent 204 to gradually open the valve, and the air inside the cuff belt flows through the air outflow vent 204 and escapes to the outside in small incremental amounts. Blood pressure is measured in the process of reducing the pressure inside the cuff belt by the incremental release of small amounts of air.
Besides the technique described in Japanese Patent No. 3029073, Japanese Laid-open Patent Application No. 2005-155898 describes a technique for enabling finer control of the flow rate through a rubber valve by providing small irregularities to the surface of the rubber valve, and managing a minute gap created by the irregularities according to the condition in which the rubber is collapsed when the rubber is pressed against a nozzle (airflow vent).